1. Field of the Invention
The present invention relates to a node (an optical dynamic burst switch) which takes advantage of optical communication, and which is included in an optical communication network which uses optical wavelengths as a communication medium for burst data transfer.
This application is based on patent applications Nos. 2001-337587, 2001-337590, 2001-337601, 2001-337891, 2001-338050, 2002-060102, 2002-060119, and 2002-060127 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
In data transfer by an IP (Internet Protocol) network, a router which acts as a node reads in the header information of an IP packet, and transfers that IP packet along a path to its destination. This is performed repeatedly between a plurality of nodes, and as a result the IP packet makes its way to the desired destination. With this type of transfer method for an IP packet it becomes necessary to read in the header information of each individual IP packet, since the transfer is performed in individual IP packet units.
On the other hand, recently, the demand has abruptly increased for high capacity transfer of consecutive data such as moving image data and the like. This type of consecutive high capacity data is termed ‘burst data’, and it is accommodated by being divided into a large number of IP packets. Since to perform transfer by individual IP packet units is inefficient for this type of burst data transfer, a cut through path is established between specified nodes, and the data transfer is performed in one stroke with this cut through path, without reading in the header information of the IP packets. In particular, it is effective to perform data transfer in this manner by using optical path.
That is, with data transfer using optical path upon a transmission path between nodes, at each node, the optical signal which has arrived after having been transmitted by optical path is temporarily converted to an electrical signal, and the header information of the IP packet is read in, and, after its destination path has been decided upon, the procedure of again converting it into an optical signal and again transmitting it to the optical path becomes necessary. By contrast to this, with data transfer using a cut through path according to wavelength path, there is no necessity to convert the optical signal to an electrical signal in order to read in the header information, and it is possible to perform burst data transfer with extremely good efficiency, since it is possible to transfer the optical signal just as it is from the start point of the cut through path until its end point.
With this type of conventional optical communication, when transferring burst data using a cut through path, it is necessary to set and fix the cut through path in advance. In order to set the cut through path in advance in this manner, a request to the effect that it is desired to establish a cut through path is made to each of the routers en route from the starting point to the end point, and the establishment of the cut through path in advance for the first time is completed by each of the routers responding to this request.
At this time, when trying to establish the settings for each of the routers for the cut through path, first, the header information of the optical IP packet which has arrived is converted into an electrical signal, and then the fact is read in as to whether or not information which corresponds to an establishment request for a cut through path is included within this header information; and, if such an establishment request is included, a wavelength is selected for cut through path establishment, and when the wavelength has been selected the cut through path establishment is actually performed. And, since it is not necessary to read in the header information of the IP packets any longer for the wavelength which has been set for the cut through path, these IP packets should be transferred as optical signals just as they are, and setting changes are performed for discriminating them from other wavelengths and handling them.
However, it requires quite a lot of time for this type of setting procedure. For example, 2t may be required for establishment the cut through path. And, if 3t is required for the transfer of the burst data using this cut through path, therefore a total of 5t is required from the establishment of the cut through path until the burst data transfer has been completed. In this example, almost half of the time period of 5t which is used for the burst data transfer is employed for establishing the cut through path. If it were possible to allot to the data transfer itself the time period which is required for establishing the cut through path in advance in this way, it would be possible to anticipate a substantial enhancement of data transfer efficiency.
Furthermore, as has been described above, in order to establish the cut through path, a request for establishing the cut through path is transmitted from the node upon the transmission side (an edge node or the like upon the transmission side) towards the node upon the receiving side (an edge node or the like upon the reception side). The request packet which contains this request is an IP packet, and it reaches the node upon the receiving side while its header information is read in by each node. If due to insufficiency of network resources or the like a problem arises with establishing the cut through path during this process, a signal which conveys the information that this has happened is transmitted towards the node upon the transmission side. When this is received at the node upon the transmission side, either the establishment of the cut through path is retried, or the process is discarded.
Furthermore, although it is desirable for the cut through path to be linked together into a single unit from the node upon the transmission side to the node upon the reception side, it may happen, depending upon the distance between the node upon the transmission side and the node upon the reception side, that deterioration of the signal quality due to loss and crosstalk upon the optical signal becomes conspicuous, in which case 3R (Reshaping, Retiming, Regenerating) processing may become necessary at one node or another, so that it becomes necessary to perform calculations in order to determine whether or not, and at which node or nodes, 3R processing should be performed.
Although in this manner a cut through path is itself most suitable for burst data transfer, it is necessary for the user who is the source of data transmission to establish the cut through path while ensuring network resources in consideration of the amount of data which he himself will attempt to transmit from now on, and there is the problem that labor and a certain time period are required for this establishment procedure.
Furthermore although, after the establishment of the cut through path has succeeded and the burst data transfer has been performed, release of this cut through path should be performed, actual release of the cut through path is not performed unless the user who is the source of data transmission transmits a release request, and the possibility is not excluded that invalid retention of a cut through path may occur.
In addition, in the conventional technology, the path over which the node upon the transmission side transmits the burst data is determined as being a particular one according to a predetermined policy. For example, if the path selection is based upon a policy of “the shortest path is taken as the most suitable path”, then the burst data is transmitted over that path for which the distance between the node upon the transmission side and the node upon the reception side is the shortest. And it is decided whether or not it is possible to ensure resources at the relay nodes upon this path.
In this manner, according to the conventional technology, it is attempted to ensure resources upon the single path which has been decided upon according to the predetermined policy, and if there is a difficulty with this ensuring of resources, even if the node upon the transmission side performs a retry, this retry will be performed for the same path as before.
In addition, although the cut through path may be the most suitable one for burst data transfer using wavelength path, during transmission the signal quality of the optical signal may deteriorate due to various factors. Accordingly, the length of a cut through path for which signal transmission without performing 3R processing is possible is inevitably limited.
In the prior act, the points at which 3R processing is to be performed are determined by calculation. In this conventional calculation for determining the points at which 3R processing is to be performed, there are two points at which problems arise. First, the factors which cause deterioration of the signal quality are various, and a large amount of data processing becomes necessary in order to perform the calculations, in consideration of these large number of factors. Accordingly, the time period required for these calculations also becomes long; this is the first problematical point. Secondly, the reliability of the results which are obtained by this type of calculation is not necessarily high, and, for safety in practice, countermeasures such as the provision of extra 3R processing points and the like are necessary, and there is the problematical point that this is not desirable from the point of view of planning in order effectively to take advantage of network resources.